1. Field of the Invention
The present invention relates to a process for producing trehalose and sugar alcohols, more particularly, to a process for producing trehalose and/or sugar alcohols from a mixture of hydrogenated saccharides containing trehalose and sugar alcohols selected from the group consisting of sorbitol, maltitol, and maltotriitol; and to a process for separating trehalose and sugar alcohols.
2. Description of the Prior Art
Trehalose, a non-reducing disaccharide composed of two glucose molecules bound at their reducing groups, is widely distributed in nature; bacteria, fungus, algae, and insects. Comparing with sucrose as a representative sweetener, trehalose is much more stable than sucrose and is superior to sucrose on sweetening quality and mildness. Thus, trehalose are now being highly required as a substitute of sucrose in the fields of foods, cosmetics, and pharmaceutical industries.
There exist two different types of methods for producing trehalose when classified on materials; the first method is one which comprises contacting starch or partial starch hydrolysates thereof with a non-reducing saccharide forming enzyme and a trehalose-releasing enzyme as disclosed in Japanese Patent Kokai Nos. 143,876/95 and 213,283/95 applied by the same applicant as the present invention, and the second method is one which comprises contacting maltose with a maltose/trehalose converting enzyme as disclosed in Japanese Patent Kokai No. 170,977/95 applied by the same applicant as the present invention. The second method has the greatest merit that it easily produces trehalose with only a single enzyme if only the material maltose is in hand. In addition, such an enzymatic reaction is an equilibrium reaction, and this results in a formation of a saccharide mixture rich in both trehalose as a reaction product and maltose as a substrate.
However, no industrial and beneficial operation method for separating trehalose from such a saccharide mixture has been established. Even column chromatographies, used most effectively to separate saccharides, could not separate trehalose and maltose having the same molecular weight as trehalose due to the fact that most of the column chromatographies are to separate saccharides based on molecular differences in saccharides.
The above saccharide composition is a mixture of non-reducing and reducing saccharides, and this greatly lowers the utility value. As described above, the method using a maltose/trehalose converting enzyme has not yet actually been used as a method for producing trehalose or saccharide mixtures containing trehalose even if the method has an advantage that it produces trehalose with only a single enzyme.
The present inventors continued studying to improve the utility value of the above saccharide composition containing non-reducing and reducing saccharides. As a result, they found that when such saccharide mixtures are subjected to hydrogenation reaction under specific conditions, such reducing saccharides including maltose are effectively converted into sugar alcohols including maltitol without substantially decomposing trehalose as a non-reducing saccharide in the mixtures, resulting in producing a highly-useful saccharide in a relatively-high yield. Based on the finding, the present inventors established saccharides with lesser reducibility, its preparation and uses, and they disclosed them in Japanese Patent Kokai No. 73,482/96. Thus, it can be said that one of the problems residing in the method using a maltose/trehalose converting enzyme was overcome.
The method as disclosed in the above publication does aim at improving the utility value of the saccharide mixtures containing trehalose and reducing saccharides such as maltose, but does not aim at separating and producing useful saccharides including trehalose. For this reason, it is expected that the establishment of a process for producing trehalose from hydrogenated saccharide mixtures, which contain trehalose and sugar alcohols and are obtainable by the method disclosed in the above publication, would explore the way for an industrial production of trehalose in which a maltose/trehalose converting enzyme is used for producing trehalose. It is also greatly expected that when once established a process for producing sugar alcohols from the hydrogenated saccharide mixtures with a relatively-high yield, this would give a more effective utility to the method using a maltose/trehalose converting enzyme.